1. Field of the Invention
This invention relates to an electric ignition type gas generation apparatus that has an ignition section that is ignited by an electric signal, and a gas generating section in which burning gas is generated by the ignition of the ignition section. This invention particularly relates to an improved electric ignition type gas generation apparatus for instantaneously operating a vehicle safety device such as a seatbelt or airbag.
2. Description of the Prior Art
Cars and other vehicles are normally provided with safety devices such as seatbelts and airbags for protecting the driver and passengers from the impact of a crash. In the case of a seatbelt system, for example, the belt is equipped with a rapid retraction means that is activated in a crash or the like to protect the wearer from the shock of the crash impact. Most such rapid retraction means are comprised of a gas generating device in which the gas is generated by the ignition of a gunpowder charge. In a crash, the shock of the impact is used to electrically or mechanically operate an igniter to ignite the gas generating material. The pressure generated by the ignition of the gas is used to instantaneously drive a cylinder piston or rotor to rapidly retract the belt.
FIG. 5 shows an example of a conventional gas generation apparatus of this type. This apparatus has a base A to which are attached an electric igniter B and a cylindrical outer casing C. As shown in FIG. 6, the electric igniter B is formed as a single unit that includes a pair of electrode pins E in a resin holder D. Each of these electrode pins E passes through the holder D, one end of each electrode pin E thereby extending out from the holder D, while the other end of each of the electrode pins E is connected to a filament or other such resistance (not shown) on a printed circuit board F. This resistance on the printed circuit board F constitutes an ignition section B'. The outer surface of the ignition section B' is covered by a priming charge G, over which is then attached a resin cup J filled with an ignition charge H. A metal casing K is fitted over the resin cup J. In the peripheral surface of the casing K is an aperture L through which the flame of the combustion propagates. The electric igniter B is inserted into a through-hole M provided in the base A and attached to the base A by means of the holder D.
The cylindrical outer casing C is formed of a metal such as aluminum or stainless steel and has a bottom that can readily be opened by the pressure of the burning gases. After being filled with the gas generating material N, the outer casing C is attached to the base A with the ignition section B' covering the igniter B. The reference symbol shown in FIG. 5 denotes a moistureproof, pressure-resistant vulcanized rubber O-ring disposed between the holder D and the base A.
When the vehicle with the gas generation apparatus having the above structure is involved in a crash, the impact of the crash is communicated as an electric signal to the electrode pins E. This causes the resistance (not shown) between the electrode pins E to heat up, igniting the priming charge G and thereby setting off the ignition charge H. When the flame of the combustion reaches gas generating material N via the aperture L, the gas generating material N starts to burn. The burning gas produced by the burning of the gas generating material N ruptures the bottom of the outer casing C and is thereby instantaneously released to the outside. The pressure generated by this burning gas instantaneously activates the seatbelt rapid retraction means or airbag.
In the conventional gas generation apparatus described above, the fact that the electric igniter B is prefabricated as a unit enables the assembly procedure to be simplified. However, in order to handle the electric igniter B as a single component, it is necessary to cover the ignition section B' with the resin cup J and the metal casing K, in addition to which the holder D that supports the electrode pins E has to be separate from the base A. Thus, this configuration markedly increases the number of parts of the gas generation apparatus, increasing the cost. Moreover, the major portion of the gas generation apparatus that includes the ignition section B' projects into the center of the outer casing C. As a result, in order to obtain the requisite gas pressure the volume of the outer casing C has to be increased, making the apparatus much larger. Also, the fact that the ignition section B' projects into the center of the outer casing C prevents the gas generating material N from burning uniformly. Therefore, to obtain the required gas pressure it is necessary to pack the outer casing C with an extra amount of gas generating material N, further increasing the size of the apparatus.
An object of the present invention is therefore to provide an electric ignition type gas generation apparatus that is smaller and less costly.